Non-Chromate Aluminum Pretreatments, Phase 2
Abstract
Current light metal finishing procedures for industrial, automotive, aerospace, and Department of Defense (DoD) applications center around the use of hexavalent chromium based chemistries for the enhancing corrosion resistance and paint adhesion. Aluminum finishing, in particular, utilizes chromate chemistries for anodizing, anodic sealing, and pretreatment (both for conversion coating aluminum substrates and for treating aluminum-based coatings deposited on steel). The most ubiquitous use of chromate coatings is in the conversion coating of aluminum alloys for use as-deposited or prior to organic coating application. These coatings are very thin, inexpensive to produce, extremely process flexible, and can be applied by immersion, spray and wipe techniques. Chromate conversion coatings offer many advantages, however, the downside is that they contain hexavalent chromium, or chromate, species that are known to be carcinogenic. The occupational safety and health issues arising from risk of worker exposure to these chemicals, as well as the costs and the potential liabilities resulting from an accidental leak to the environment and waste disposal issues from normal finishing operations are making the use of chromate-based conversion coatings unattractive to the metal finishing industry. Additionally, proposed Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) changes for hexavalent chromium would make the use of chromate very costly. A final ruling on the PEL is scheduled for the beginning of 2006, and under the current proposal, would drop the PEL from 100 g/m3 (for hexavalent chromium in the form of chromic acid) to 10 g/m3 at the highest; or possibly as low as 0.5 or 1 g/m3. This change would be especially hard for medium to small sized plating and coating contractors to comply with in a cost-effective manner.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2004
- Accession Number
- ADA607454
Entities
People
- Bill Nickerson
Organizations
- Naval Air Systems Command